1. Field of the Invention
The invention is in the field of dental treatment trays used to deliver oral treatment compositions.
2. Background Technology
A common bleaching method involves the use of custom dental trays, which conform to the shape of each user's unique dentition. One way to form a customized tray is by vacuum forming a sheet of a moisture resistant thermoplastic polymer over a stone cast or model of a person's teeth and then trimming excess tray material. Another uses a person's teeth as the template (e.g., “boil-and-bite” trays). Customized dental trays prepared and sold by dentists are formed using a stone model of a patient's teeth and typically cost hundreds or even thousands of dollars.
Other methods involve flexible strips and non-customized trays and that can approximate differently sized and shaped dental arches and which are substantially less expensive than customized trays to manufacture. A dental bleaching composition is placed onto the strip or into the tray, which is then placed over the person's teeth for a desired period of time. To install a bleaching strip, a portion of the bleaching strip is placed over the front surfaces of the user's teeth, and the remainder is folded around the occlusal edges of the teeth and against a portion of the lingual surfaces. Because of the generally poor adhesion of bleaching strips to the user's teeth and their generally flimsy nature, it is often difficult for the user to maintain the bleaching strip in its proper position for the recommended time. Conventional bleaching strips are prone to slip off the teeth as a result of even minimal movement of the user's mouth, jaw or tongue. In some cases, the bleaching strip can become so dislodged or mangled that it must be removed by the user and replaced with a fresh bleaching strip to complete the recommended bleaching time.
Non-custom dental trays generally suffer from poor adaptability to the user's teeth. Although some non-custom dental trays are sufficiently flexible to generally adapt to differently sized and shaped dental arches within a certain range of sizes and shapes, existing non-custom trays, particularly trays that are used without an outer support tray and therefore must be self-supporting, are unable to comfortably adapt to dental arches of exaggerated size or shape (i.e., teeth that are unusually large, small or not particularly straight). Moreover, existing self-supporting trays have difficulty in adapting and conforming to the ridges, depressions and contours of a person's individual teeth in addition to adapting to the general shape and size of the person's dental arch. As a result of these failures, large gaps can easily form between the non-custom tray wall and the person's teeth during use, especially in the spaces between individual teeth, as a result of forming a bridge that spans between the outermost surfaces of adjacent teeth and/or the inability of the tray wall to accurately adapt to all the teeth in a row instead of simply accommodating the largest or most crooked teeth. Such gaps facilitate the invasion of saliva into the dental tray and/or expulsion of the dental bleaching composition from the dental tray during use.
Moreover, the inability of the front and rear walls of existing non-custom trays to adapt and conform to the ridges, depressions and contours of a person's individual teeth means that a substantial portion of each wall tends to move in unison as a result of external pressures (e.g., the person's lips or tongue pressing on the outer surface of a tray wall). Movement of a localized region of a self-supporting tray adjacent to one tooth typically causes simultaneous movement of the tray wall in adjacent regions where such movement may be undesired. In addition to forming large gaps, this may create a pumping action that exacerbates the aforementioned tendency of saliva to invade gaps between the tray walls and the person's teeth and/or bleaching composition to be expelled from the dental tray.
U.S. Pat. Nos. 6,964,571 and 7,004,756 (“Andersen patents”) disclose self-supporting, non-custom dental trays made from thermoplastic materials such as low density polyethylene (LDPE), ultra low density polyethylene (ULDPE), ethylene-vinyl acetate copolymer (EVA), polycaprolactone (PCL), other types of polyethylene (PE), polypropylene (PP), polyesters, polycarbonates, polyamides, polyurethanes, polyesteramides, and copolymers thereof. The foregoing materials, when used to manufacture dental treatment trays that are relatively thick (i.e., greater than 2 mm), yield trays that are quite rigid and non-adaptable to the user's teeth absent customization. Therefore, Andersen discloses non-custom, self-supporting trays which are thin-walled (i.e., less than about 1 mm). This makes them sufficiently flexible so as to conform to a range of differently sized and shaped dental arches without the need for formal customization. While the self-supporting trays of Andersen represent an important advancement in the art compared to previously existing self-supporting dental trays, such trays do not readily and accurately adapt and conform to the ridges, depressions and contours of a person's individual teeth. Instead, they generally form a bridge between individual teeth that can span across the depressions between teeth. They also have tray wall regions that tend to move in partial unison rather than adapting themselves to the contours of individual teeth.
Moreover, the ability to injection mold dental trays from the types of thermoplastic materials disclosed in the Andersen patents is limited (i.e., there is a practical limit as to the thinness that such trays can be successfully injection molded). Accordingly, very thin-walled dental trays (i.e., less than about 5 mm) must be formed by other methods, such as vacuum forming a thin polymer sheet over a template.
In an attempt to improve upon the manufacturing process of Andersen, U.S. Pat. No. 7,137,814 (“Fischer patent”) taught the inclusion of a substantial quantity (e.g., 20-50% by weight) of a hydrophobic oil plasticizer (e.g., mineral oil). The inclusion of a relatively large quantity of plasticizer greatly decreased the thickness at which dental trays could be injection molded. For example, trays having a wall thickness of less than about 0.015 inch (or about 0.4 mm) could, for the first time, be manufactured according to the Fischer patent. Moreover, the inclusion of a plasticizer such as mineral oil yielded dental trays that were softer and more flexible than dental trays made from non-plasticized thermoplastic polymers. Nevertheless, it was found that even hydrophobic plasticizers such as mineral oil tend to bloom (i.e., migrate to the surface) over time. Such blooming yields dental trays having poor taste and a surface to which hydrophilic dental bleaching compositions could not readily adhere. The inability of a sticky dental bleaching composition to readily adhere to the tray surface generally decreases adaptability and conformability of the tray to the person's teeth.
Ultimately, the main impediment to successful bleaching is the failure of users to complete the prescribed bleaching regimen. If the bleaching apparatus is difficult to install over a person's teeth, requires numerous repetitions to achieve observable results, or is uncomfortable to wear, the user may simply give up and prematurely abort the prescribed bleaching regimen. Thus, even if dental bleaching is possible using a particular bleaching apparatus or method, it is less likely to occur if the inadequacies of the bleaching apparatus or method cause a user to become discouraged before desired results are attained. One commercially successful pre-filled, self-supporting tray device manufactured according to Andersen has been a great success. Customer satisfaction has generally been high. Nevertheless, the main complaint of such devices is their inability to conform and adapt to the user's teeth like a custom tray.
As a result, the use of expensive customized dental trays remains the most reliable dental bleaching method in terms of regimen completion and results. Non-custom, over-the-counter bleaching strips and trays, while relatively inexpensive, generally provide inferior results compared to custom-fitting trays.